Super-absorbent swellable hot melt coated optical fibers, buffer tubes, cable designs thereof and manufacturing processes

ABSTRACT

Embodiments of an optical fiber cable are provided. The cable includes a cable jacket and at least one buffer tube. Each buffer tube surrounds a plurality of optical fibers. The cable jacket surrounds the at least one buffer tube. Further, a coating of superabsorbent, swellable hot melt is applied to at least one of the following locations: (i) along at least a portion of the length of at least one of the plurality of optical fibers; (ii) along at least a portion of the length of the exterior or interior surface of the at least one buffer tube; or (iii) along at least a portion of the length of the interior surface of the cable jacket. Moreover, the superabsorbent, swellable hot melt is capable of absorbing at least 50 g of water per gram of superabsorbent, swellable hot melt.

PRIORITY APPLICATIONS

This application is a divisional of U.S. application Ser. No. 16/686,290filed on Nov. 18, 2019, which is a continuation of InternationalApplication No. PCT/US18/34686, filed on May 25, 2018, which claims thebenefit of priority to U.S. Application No. 62/513,033, filed on May 31,2017, both applications being incorporated herein by reference.

BACKGROUND

The disclosure relates generally to cables and more particularly tooptical fiber cables having a coating of superabsorbent, swellable hotmelt on at least one of the interior of a cable jacket, the interior orexterior of a buffer tube, or along the length of an optical fiber.Optical cables have seen increased use in a wide variety of field'sincluding various electronics and telecommunications fields. Opticalcables contain or surround one or more optical fibers. The cableprovides structure and protection for the optical fibers within thecable.

SUMMARY

In one aspect, embodiments of an optical fiber cable are provided. Theoptical fiber cable includes a cable jacket having an exterior surfaceand an interior surface and at least one buffer tube. Each of the atleast one buffer tube has an exterior surface and an interior surface,and each of the at least one buffer tube surrounds a plurality ofoptical fibers. The cable jacket surrounds the at least one buffer tube.Further, a coating of superabsorbent, swellable hot melt is applied toat least one of the following locations: (i) along at least a portion ofthe length of at least one of the plurality of optical fibers; (ii)along at least a portion of the length of the exterior or interiorsurface of the at least one buffer tube; or (iii) along at least aportion of the length of the interior surface of the cable jacket.Moreover, the superabsorbent, swellable hot melt is capable of absorbingat least 50 g of water per gram of superabsorbent, swellable hot melt.

In another aspect, embodiments of a method of fabricating an opticalfiber cable are provided. The method includes the steps of applying acoating of superabsorbent, swellable hot melt along at least a portionof a length of an optical fiber and arranging within a buffer tube aplurality of optical fibers. At least one of the plurality of opticalfibers is an optical fiber having the coating. Further, the opticalfibers are arranged such that a gap between any two adjacent opticalfibers is less than a diameter of any one of the plurality of opticalfibers.

In still another aspect, embodiments of another optical fiber cable areprovided. The optical fiber cable includes a cable jacket having anexterior surface and an interior surface and at least one buffer tube.Each of the at least one buffer tube has an exterior surface and aninterior surface, and the at least one buffer tube is surrounded by theouter cable jacket. The optical fiber cable also includes a plurality ofoptical fiber ribbons arranged in a stack within each of the at leastone buffer tube. Each of the optical fiber ribbons includes a pluralityof optical fibers surrounded by and supported within a polymeric ribbonmatrix. Further, a coating of superabsorbent, swellable hot melt isapplied to at least one of the following locations: (i) along at least aportion of the length of at least one of the plurality of optical fiberribbons; (ii) along at least a portion of the length of the exterior orinterior surface of the at least one buffer tube; or (iii) along atleast a portion of the length of the interior surface of the cablejacket. The superabsorbent, swellable hot melt is capable of absorbingat least 50 g of water per gram of superabsorbent, swellable hot melt.

Additional features and advantages will be set forth in the detaileddescription that follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing theembodiments as described in the written description and claims hereof,as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary, and areintended to provide an overview or framework to understand the natureand character of the claims.

The accompanying drawings are included to provide a furtherunderstanding and are incorporated in and constitute a part of thisspecification. The drawings illustrate one or more embodiment(s), andtogether with the description serve to explain principles and theoperation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification illustrate several aspects of the present invention and,together with the description, serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a cross-sectional view of an optical fiber cable usable withthe superabsorbent, swellable hot melt (SA-SHM), according to anexemplary embodiment;

FIG. 2 is a cross-sectional view of a buffer tube having a lining ofSA-SHM and containing optical fibers also having a coating of SA-SHM,according to an exemplary embodiment;

FIG. 3A is a partial isometric view of an optical fiber with a coatingof SA-SHM that is discontinuous along its length, according to anexemplary embodiment;

FIG. 3B is a cross-sectional view of an optical fiber with a coating ofSA-SHM that is discontinuous around its circumference, according to anexemplary embodiment;

FIG. 4 is a cross-sectional view of an optical fiber cable with theoptical fibers arranged in ribbons, each ribbon having a coating ofSA-SHM, according to an exemplary embodiment; and

FIG. 5 is a graph representing the water swelling capacity of threeSA-SHM as a function of time, according to an exemplary embodiment.

While the invention will be described in connection with certainpreferred embodiments, there is no intent to limit it to thoseembodiments. On the contrary, the intent is to cover all alternatives,modifications and equivalents as included within the spirit and scope ofthe invention as defined by the appended claims.

DETAILED DESCRIPTION

Referring generally to the figures, various embodiments of an opticalfiber cable having one or more cable component coated withsuperabsorbent, swellable hot melt (SA-SHM) are shown. In embodiments,the use of SA-SHM helps to alleviate issues with bend losses experiencedby optical fiber cables in their various deployments, particularly thosethat utilize superabsorbent polymer particles. In particular, the SA-SHMis used as a coating on the inside of a optical fiber cable jacket, as acoating on or inside buffer tubes, as a coating along at least a portionof the length of at least one optical fiber, and/or as a coating on aleast a portion of the length of at least one ribbon of an optical fibercable. Furthermore, cables using the SA-SHM do not requiresuperabsorbent polymer (SAP) powders, SAP tapes, and/or SAP yarns, whichare a source of bend loss.

As shown in FIG. 1 , an optical cable, shown as cable 10, is illustratedaccording to an exemplary embodiment. Cable 10 includes an outer cablejacket, shown as outer jacket 12, having an inner surface 14 thatdefines an inner passage or cavity, shown as central bore 16, and anouter surface 18 that generally defines the outermost surface of cable10. As will be generally understood, inner surface 14 of jacket 12defines an internal area or region within which the various cablecomponents discussed herein are located.

In various embodiments, cable jacket 12 is formed from an extrudedthermoplastic material, which is not a superabsorbent polymer material.In various embodiments, cable jacket 12 may be a variety of materialsused in cable manufacturing such as polyethylene, medium densitypolyethylene, polyvinyl chloride (PVC), polyvinylidene difluoride(PVDF), nylon, polyester or polycarbonate and their copolymers. Inaddition, the material of cable jacket 12 may include small quantitiesof other materials or fillers that provide different properties to thematerial of cable jacket 12. For example, the material of cable jacket12 may include materials that provide for coloring, UV/light blocking(e.g., carbon black), burn resistance, etc.

Cable 10 includes one or more optical transmission elements or opticalwaveguides, shown as optical fibers 20. In the embodiment shown, groupsof optical fibers 20 are located in separate buffer tubes 22, and buffertubes 22 are wrapped (e.g., in an SZ stranding pattern) around a centralstrength member 24. In various embodiments, cable 10 includes at leastfour buffer tubes 22. Central strength member 24 may be any suitableaxial strength member, such as a glass-reinforced plastic rod, steelrod/wire, etc. Generally, cable 10 provides structure and protection tooptical fibers 20 during and after installation (e.g., protection duringhandling, protection from elements, protection from the environment,protection from vermin, etc.).

In various embodiments, cable 10 also includes an armor layer, shown asarmor 26. In general, armor 26 is formed from a strip of metal material(e.g., a metal tape, a flat elongate continuous piece of material, etc.)that is wrapped around and circumferentially surrounds buffer tubes 22.As shown in FIG. 1 , armor 26 is located adjacent to the inner surface14 of outer jacket 12 such that these two layers are in contact witheach other. In specific embodiments, armor 26 is corrugated steel tapematerial that is wrapped around the interior portions of cable 10, andin some of these embodiments, armor 26 is longitudinally folded forminga longitudinal overlapped section where opposing edges of the tapeoverlap to completely surround inner buffer tubes 22 (and any otherinterior component of cable 10). In other embodiments, armor 26 may be astrip of metal tape material, helically wrapped around buffer tubes 22such that armor 26 forms a layer circumferentially surrounding buffertubes 22. In general, armor layer 26 provides an additional layer ofprotection to fibers 20 within cable 10, and may provide resistanceagainst damage (e.g., damage caused by contact or compression duringinstallation, damage from the elements, damage from rodents, etc.).Cable 10 may include a variety of other components or layers, such ashelically wrapped binders, circumferential constrictive thin-filmbinders, etc.

In the embodiment shown, cable 10 includes one or more preferential tearfeature and/or ripcord 28 embedded in or underneath jacket 12. In thisembodiment, the preferential tear feature and/or ripcord 28 is locatedwithin jacket 12 such that ripcord 28 facilitates opening of outerjacket 12. In some embodiments, ripcord 28 may be located within armorlayer 26 such that ripcord 28 facilitates opening of both armor 26 andjacket 12.

In embodiments, cable 10, optical fibers 20 and buffer tube 22 areconfigured in various ways to provide a high fiber density and highfiber count cable while at the same time reducing or minimizing buffertube size and/or cable jacket size. As discussed herein, low diameteroptical fiber allows higher density and smaller cable, and the low bendloss design of these optical fibers allows such high density, smallcables to have acceptable signal loss properties.

In addition, bend losses may be greater in cables in which opticalfibers are densely packed in relatively rigid buffer tubes, are denselypacked within a cable jacket and/or are densely packed in an opticalfiber ribbon arrangement. Bend losses in such cables are caused, atleast in part, by positional constraint resulting from the dense packingwhich limits the ability of optical fibers to shift to assume low strainpositions during bending, compression, etc. For example, in certainoptical fiber cables using SAP powder as a means to absorb water, theSAP powder particles can, in some circumstances, cause microbending ofthe optical fibers 20 particularly when the optical fibers 20 aredensely packed, which can result in undesirable attenuation. That is, insome optical fiber cables, the geometry (generally, shard-like) and size(>100 microns) of the SAP powder particles can, in some circumstances,cause microbending in densely packed optic fibers and prevent theoptical fibers from assuming low strain positions. Thus, typical opticalfiber cable and/or buffer tube configurations include a significantamount of free-space between the outer surfaces of the optical fibersand the inner surface of the buffer tube or jacket, and this free-spaceallows the optical fibers to move or shift to assume low strainpositions during bending. By reducing strain that the optical fibersexperience during bending, such low density cables provide asatisfactory level of signal attenuation, but do so with a relativelylarge diameter buffer tube and/or relatively large cable jacket.

By comparison, in the embodiment depicted in FIG. 2 , the buffer tube 22surrounds densely packed optical fibers 20. In an embodiment, a diameterratio parameter Q is defined between the inner diameter D1 of the buffer22 and an outer diameter D2 of each of N number of optical fibers 20(i.e., Ω=D1/D2). In a specific embodiment, the diameter ratio parameterΩ is selected such that 2.25+0.143(N)≤Ω≤1.14+0.313(N). In embodiments,the number N of optical fibers 20 is at least four. In specificembodiments, the number N of optical fibers 20 is 12, the inner diameterD1 of the buffer tube is 15 mm, and the outer diameter D2 of eachoptical fiber 20 is less than 210 microns and greater than 100 microns.In another embodiment in which the number N of optical fibers 20 isgreater than 6, the diameter ratio parameter Ω is selected such thatΩ≤2.66+0.134(N).

In still other embodiments, the optical fibers 20 are arranged in such away that a gap G between adjacent optical fibers 20 is smaller than thediameter D2 of any individual optical fiber 20. Additionally, the gapbetween any optical fiber 20 and the interior surface of the buffer tube22 is smaller than the diameter D2 of any individual optical fiber 20.That is, the optical fibers 20 are arranged within the buffer tube 22 insuch a way that no space large enough to accommodate an additionaloptical fiber 20 is provided within the buffer tube 22.

The packing of the optical fibers 20 within the buffer tube in thepreviously described manners is facilitated by an SA-SHM coating 30 thatis applied at least partially around and at least partially along thelength of at least one of the optical fibers 20. Thus, while all of theoptical fibers 20 of the embodiment depicted in FIG. 2 are depicted withthe SA-SHM coating 30, embodiments exist where only one, two, three,etc. optical fibers 20 have the SA-SHM coating 30, and the remainingoptical fibers 20 remain uncoated. In such embodiments, the SA-SHMcoating 30 on only some of the optical fibers 20 is enough to providewater protection for all the optical fibers 20 within the buffer tube22. Advantageously, the SA-SHM coating 30 does not contribute tomicrobending losses in the same manner as SAP powders, water blockingtapes or SAP tapes, and/or SAP yarns, which means that the opticalfibers 20 can be placed closer together within the buffer tube 22without the concern of providing a substantial amount of space for theoptical fiber communication elements to move into low strain positions.

In other embodiments, the SA-SHM coating 30 is located on the interiorsurface of the buffer tube 22. In such an embodiment, the SA-SHM coating30 can be applied to a bundle of optical fibers 20, such as by spraying,atomizing, dip-coating, extruding, fiberizing, etc. the SA-SHM coating30 on the bundle of fibers 20 or by co-extruding the SA-SHM coating 30with the buffer tube 22. In another embodiment, the SA-SHM coating 30 islocated on the exterior surface of the buffer tube 22. In such anembodiment, the SA-SHM 30 can be applied to the exterior surface of thebuffer tube 22 by spraying, atomizing, dip-coating, extruding,fiberizing, etc. or by co-extruding the SA-SHM coating 30 with thebuffer tube 22. In still another embodiment, the SA-SHM coating 30 isapplied to the interior surface 14 of the cable jacket 12, such asbetween the cable jacket 12 and the armor 26 (if included). In such anembodiment, the SA-SHM coating 30 can be applied to a bundle of buffertubes 22, such as by spraying, atomizing, dip-coating, extruding,fiberizing, etc. the SA-SHM coating on the bundle of buffer tubes 22 orby co-extruding the SA-SHM coating 30 with the cable jacket 12.

Regardless of location, the SA-SHM coating 30 can have a thicknesst_(hm) of up to 200 microns in some embodiments. In other embodiment,the SA-SHM coating 30 has a thickness of up to 50 microns, and in stillother embodiments, the SA-SHM coating 30 has a thickness of up to 30microns. The SA-SHM coating also has a thickness of at least 1 micron inembodiments.

The SA-SHM coating 30 can have various compositions. However, generally,the water absorption capacities of the SA-SHM coatings used in theembodiments of the optical fiber cables disclosed herein will be greaterthan 50 grams of water absorbed per gram of SHM coating. In otherembodiments, the water absorption capacity of the SHM coating is greaterthan 100 gram of water absorbed per gram of SHM coating. In still otherembodiments, the water absorption capacity of the SHM coating is greaterthan 150 grams of water absorbed per gram of SHM coating. In yet otherembodiments, the water absorption capacity of the SHM coating is greaterthan 200 grams of water absorbed per gram of SHM coating.

In embodiments, the SA-SHM coating is comprised of a hot melt matrix inwhich one or more superabsorbent polymer powders are suspended. That is,the superabsorbent polymer powders are distributed throughout thethickness of the hot melt matrix and not just on a surface of the hotmelt or not just to a certain depth of the hot melt. The hot melt matrixadditionally provides a connective matrix by which to keep the coatingtogether when the superabsorbent polymer powders expand upon contactingwater.

In some embodiments, the SA-SHM coatings used are physically settingthermoplastic materials. For example, these may include commerciallyavailable water-swellable hot melt adhesives such as HM002 and HM008B(available from Stewart Superabsorbents, Hickory, N.C.), Technomelt AS4415 (also known as Macromelt Q 4415 available from Henkel Corp.,Madison Heights, Mich.), and NW1117 and NW1120B (Hydrolock® superabsorbent thermoplastic available from H. B. Fuller Company, VadnaisHeights, Minn.).

Additionally, a variety of exemplary compositions are provided in thefollowing paragraphs. According to one embodiment, the SA-SHM coatingincludes essentially three components that are mixed homogenously. Thefirst component is a water-insoluble component containing at least onewater-insoluble polymer or copolymer and at least one othersubstantially water-insoluble resin. For example, the first componentcan be selected from polyamides, copolyamides, polyaminoamides,polyesters, polyacrylates, polymethacrylates, polyolefins andethylene/vinyl acetate (EVA) copolymers. Further the first component canbe mixtures of one or more of the foregoing polymers. The secondcomponent is a water-soluble or water-dispersible component containingat least one water-soluble or water-dispersible oligomer and/or polymeror copolymer. For example, the second component can be selected frompolyethylene glycols with molecular weights of 400 to 20,000, polyvinylmethyl ether, polyvinyl pyrrolidone, copolymers of vinyl methyl ether orvinyl pyrrolidone, polyvinyl alcohols, water-soluble orwater-dispersible polyesters or copolyesters, and water-soluble orwater-dispersible acrylate polymers.

The third component is a water-swellable component (i.e., asuperabsorbent polymer) consisting of a water-swellable homopolymer orcopolymer. For example, the third component can be selected from anyhomopolymers and/or copolymers which, as hydrophilic materials, arecapable of absorbing and retaining large amounts of water, even underpressure, without immediately dissolving in the water, including, forexample, graft copolymers of starch or cellulose with acrylonitrile,acrylic acid or acrylamide, carboxymethyl cellulose, maleicanhydride/poly-α-olefin copolymers, polyacrylamide, polyacrylic acid andsalts of polyacrylic acid, and, optionally, copolymers of acrylic acidor acrylamide with acrylate esters. In embodiments, other suitable thethird components include homopolymers and copolymers of acrylic acid ormethacrylic acid, acrylonitrile or methacrylonitrile, acrylamide ormethacrylamide, vinyl acetate, vinyl pyrrolidone, maleic acid, maleicanhydride, itaconic acid, itaconic anhydride, vinyl sulfonic acid orhydroxyalkyl esters of such acids, 0 to 95% by weight of the acid groupsbeing neutralized with alkali or ammonium groups and thesepolymers/copolymers are crosslinked by means of polyfunctionalcompounds. Graft copolymers of starch or cellulose with the abovecomonomers can also be used in certain embodiments. Still other suitablesuperabsorbent polymers include crosslinked acrylate polymers,crosslinked products of vinyl alcohol-acrylate copolymers, crosslinkedproducts of polyvinyl alcohols grafted with maleic anhydride,cross-linked products of acrylate-methacrylate copolymers, crosslinkedsaponification products of methyl acrylate-vinyl acetate copolymers,crosslinked products of starch acrylate graft copolymers, crosslinkedsaponification products of starch acrylonitrile graft copolymers,crosslinked products of carboxymethyl cellulose polymers, andcrosslinked products of isobutylene-maleic anhydride copolymers.

In some embodiments, the SA-SHM also includes a tackifying resin orresins to increase the tackiness of the melt. In particular embodiments,various colophony derivatives, i.e., in particular the resin esters ofabietic acid, are used for the tackifying resin; although, in otherembodiments, other polyterpenes and terpene/phenol resins are used.Other colophony derivatives include colophony esters of various mono-and poly-functional alcohols. Additionally, suitable tackifying resinsinclude wood rosin, tall oil rosin, tall oil derivatives, gum rosin,rosin ester resins, natural terpenes, synthetic terpenes, and petroleumbased tackifying agents, including, e.g., aliphatic, aromatic and mixedaliphatic-aromatic petroleum based tackifying resins. Still further,other suitable tackifying resins include, e.g., alpha-methyl styreneresins, branched and unbranched C₅ resins, C₉ resins and C₁₀ resins,styrenic and hydrogenated modifications thereof, and combinationsthereof.

In particular embodiments, the SA-SHM coating contains the followingcomponents: 15 to 45% by weight of resin esters or terpene/phenolresins; 15 to 40% by weight of thermoplastic copolymer, moreparticularly ethylene/vinyl acetate copolymer; 5 to 20% by weight ofacrylate copolymers; 5 to 30% by weight of polyethylene glycols; 5 to15% by weight of polyvinyl ethyl ethers, water-soluble orwater-dispersible acrylate polymers or water-soluble orwater-dispersible copolyesters; 15 to 50% by weight of powder-formpolyacrylic acid salt, polyacrylamide or similar powdered superabsorbentpolymer; and 0.2 to 2.0% by weight of stabilizers, such as, for example,antioxidants based on sterically hindered phenols, that enhance thetemperature stability of the compositions.

In other particular embodiments, the SA-SHM contains the followingcomponents: 15 to 45% by weight of resin esters, terpene/phenol resinsor the like; 15 to 40% by weight of thermoplastic polymer or copolymer,more particularly ethylene/vinyl acetate copolymer; 5 to 25% by weightof polyethylene glycols; 15 to 50% by weight of a powderedsuperabsorbent polymer, more particularly polyacrylic acid salt; 0.2 to2.0% by weight of a stabilizer; and 0.5 to 5.0% by weight of waxes, moreparticularly ethylene bis-stearamide.

In another embodiment of a suitable SA-SHM coating composition, theSA-SHM coating is comprised of 10 to 25% by weight of at least onetackifying resin, 20 to 40% by weight of at least one water-dispersibleEVA wax, 5 to 25% by weight of at least one ethylene/acrylic acidcopolymer, 15 to 35% by weight of at least one water-soluble homopolymeror copolymer, and 20 to 40% by weight of at least one powderedsuperabsorbent polymer having an average particle size of less than 80microns.

The tackifying resins can be selected from the same group of tackifyingresins discussed above. The water-dispersible EVA waxes are selectedfrom polyethylene waxes based on an ethylene/vinyl acetate copolymerhaving a vinyl acetate content of up to 15% and molecular weights ofbetween 500 and about 10,000. Flexibilizing ethylene copolymers,particularly ethylene/alkyl acrylate copolymers having an alkyl acrylateproportion of 15 to 40% by weight, are suitable as hydrophobic matrixcomponents for binding the powdered superabsorbent polymer. Longer-chainalkyl acrylic esters are particularly suitable as comonomers in thisrespect, particularly the C₄-C₁₂ alkyl acrylates.

The water-soluble homopolymer or copolymer can include polyethyleneglycol, ethylene oxide/propylene oxide copolymers (either as blockcopolymers or as random copolymers having a predominate proportion ofethylene oxide), polyvinyl methyl ether, polyvinyl pyrrolidone,polyvinyl alcohol, and copolymers of such monomers with otherolefinically unsaturated monomers. In embodiments, these water-solublepolymers have molecular weights of between 1000 and 20,000, they may beliquid at room temperature, or they may be solid and waxy in cases wherehigher molecular weights are used. Suitable powdered superabsorbsentpolymers include those listed above.

In still another embodiment, the SA-SHM is comprised of 1% to 25% byweight of a block copolymer, 45% to 75% by weight of a powderedsuperabsorbent polymer, 15% to 40% by weight of a plasticizing oil, andoptionally 1% to 5% by weight of a surfactant. Suitable block copolymersinclude linear and radial copolymer structures having the formula (A-B)xor A-B-A, where block A is a polyvinylarene block, block B is apoly(monoalkenyl) block, and x is an integer of at least 1. Suitableblock A polyvinylarenes include, e.g., polystyrene,polyalpha-methylstyrene, polyvinyltoluene and combinations thereof.Suitable B blocks include, e.g., conjugated diene elastomers including,e.g., polybutadiene and polyisoprene, hydrogenated elastomers,ethylene/butylene (hydrogenated butadiene) and ethylene/propylene(hydrogenated isoprene), and combinations and mixtures thereof. Suitablepowdered superabsorbent polymers include those listed above.

Suitable plasticizing oils include, e.g., hydrocarbon oils low inaromatic content, mineral oil. In a particular embodiment, theplasticizing oils are paraffinic or naphthenic. In some embodiments, theSA-SHM can also include tackifying agents, such as those listed above,up to 40% by weight.

In an embodiment, the SA-SHM coating includes at least one of sodium orpotassium sodium acrylate or acrylamide copolymers, cross-linkedcarboxymethylcellulose, ethylene maleic anhydride copolymers,cross-linked polyethylene oxide, polyvinyl alcohol copolymers, orstarch-grafted copolymers of polyacrylonitrile.

Referring to each of the above described SA-SHM coating compositions, inembodiments, the average particle size of the superabsorbent polymerpowders is between 1 micron and 100 microns. Broadly, in embodiments,the average particle size of the superabsorbent polymer powder is lessthan or equal to 80 microns. In other embodiments, the average particlesize of the superabsorbent polymer powders is less than or equal to 50microns. In still other embodiments, the average particle size of thesuperabsorbent polymer powders is less than or equal to 38 microns, andin yet other embodiments, the average particle size of thesuperabsorbent polymer powders is less than or equal to 25 microns.Further, in embodiments, the average particle size of the superabsorbentpolymer powders is greater than 1 micron, and in other embodiments, theaverage particle size of the superabsorbent polymer powders is greaterthan 10 microns. Additionally, in embodiments, less than 50% of thesuperabsorbent polymer powder particles have a maximum outerdimension≥50 microns. In still other embodiments, less than 10% of thesuperabsorbent polymer powder particles have a maximum outerdimension≥38 microns, and in yet other embodiments, less than 10% of thesuperabsorbent polymer powder particles have a maximum outerdimension≥25 microns. Further, in embodiments, the superabsorbentpolymer powders have particles that are spherical in shape.

Additionally, in some embodiments, low-smoke, zero halogen (LSZH) and/orother fire retardant additives are added to the SA-SHM. Exemplary fireretardant additives include aluminum trihydrate, magnesium hydroxide,smoke suppressant molybdenum-based particles, ammonium polyphosphate,and pentaerythritol.

As mentioned above, the SA-SHM coating can be applied to the innersurface 14 of the cable jacket 12, to the exterior or interior surfaceof the buffer tubes 22, and/or to the optical fibers 20. The SA-SHM canbe applied to these surfaces via a variety of application methods. Inexemplary embodiments, the SA-SHM is applied to the jacket 12, buffertubes 22, and/or optical fibers 20 by atomizing, fiberizing, dipcoating, spray, or by co-extrusion (e.g., extruding the coating 30 atthe same time as the cable jacket 12, buffer tube 22, and/or jacket forthe optical fiber 20). Thus, the multitude of different applicationmethods provides low cost and flexible manufacturing. Further, thecomponents of the optical fiber cables can be coated at different stagesin the manufacturing process, thereby enabling more options for custommanufacturing. Further, the application of the SA-SHM coating is notlimited with respect to buffer tube or cable length (i.e., the SA-SHMcoating can continuously be applied to the cable component regardless ofthe length of that component).

Indeed, in embodiments, the SA-SHM coating 30 is applied continuouslyalong the entire length or at least a substantial portion of the entirelength of the cable jacket 12, buffer tube 22, and/or optical fiber 20.However, in another embodiment, the coating 30 is applieddiscontinuously. In an exemplary embodiment shown in FIG. 3A, thecoating 30 is applied discontinuously along the length of an opticalfiber 20 (while not depicted, the coating 30 can also be applieddiscontinuously along the length of the cable jacket 12 and/or buffertube 22). As can be seen, the optical fiber 20 has alternating coatedsections 36 and uncoated sections 38 (only one uncoated section 38 isdepicted in FIG. 3A). The first coated section 36 has a length d1,followed by an uncoated section 38 having a length d2, which is followedby another coated section 36 having a length d3. In embodiments, thelengths d1, d2, and d3 are the same length; however, in otherembodiments, the lengths d1, d2, and d3 are different lengths. Further,in embodiments, the lengths d1 and d3 of the coated sections 36 can bethe same length, which is different than the length d2 of the uncoatedsection. In embodiments, the lengths d1, d2, and d3 are all between 1 mmand 500 mm in length. In another embodiment, the lengths d1, d2, and d3are all between 1 mm and 100 mm in length.

Additionally, the SA-SHM coating 30 can be applied discontinuouslyaround the interior circumferential surface of the cable jacket 12,discontinuously around the exterior or interior circumferential surfaceof the buffer tube 22, and/or discontinuously around the exteriorcircumferential surface of the optical fiber 20. FIG. 3B provides anexemplary embodiment of an optical fiber 20 with a discontinuous coating30 (while not depicted, the coating 30 can also be applieddiscontinuously around the inner circumference of the cable jacket 12and/or buffer tube 22). As can be seen in the cross-sectional view ofthe embodiment depicted in FIG. 3B, the optical fiber 20 includes a coreregion 40 along which optical signals travel, a cladding region 42 thatkeeps the optical signals substantially within the core region 40, andan optical fiber jacket 44. In the embodiment depicted, the coating 30is applied over the optical fiber jacket 44; however, in otherembodiments, the coating 30 can be applied on the exterior surface ofthe cladding region 42. As shown in FIG. 3B, the optical fiber 20 has acoated section 36 and an uncoated section 38. In embodiments, the coatedsection 36 covers between 5% and 75% of the circumference of the opticalfiber 20. In another embodiment, the coated section 36 covers between 5%and 50% of the circumference of the optical fiber 20, and in stillanother embodiment, the coated section 36 covers between 5% and 25% ofthe circumference of the optical fiber 20.

In still another embodiment, the coating 30 is discontinuous along thelength and around the circumference of the interior surface of the cablejacket 12, the exterior or interior surface of the buffer tube 22,and/or the optical fiber 20.

Additionally, in another embodiment, the coating 30 is applied in anoptical fiber ribbon cable 50. Referring to FIG. 4 , an optical fiberribbon cable 50 is shown according to an exemplary embodiment. Cable 50is substantially the same as cable 10 (as shown in FIG. 1 ) except asdiscussed herein. As shown in FIG. 4 , cable 50 includes a single buffertube 52, and a stack 54 of a plurality of optical fiber ribbons 56. Eachoptical fiber ribbon 56 includes a plurality of optical fibers 20surrounded by and supported by a polymeric matrix 58. In variousembodiments, cable 50 includes at least four ribbons within stack 54 andeach ribbon 56 supports four optical fibers 20. Similar to the previousembodiments, the SA-SHM coating 30 is applied to at least one of thefollowing locations within the cable 50: at least partially along thelength of at least one of the optical fiber ribbons 56 in the buffertube 52, at least partially along the length of the exterior or interiorsurface of the buffer tube 52, or at least partially along the length ofthe interior surface of the cable jacket 12. Additionally, inembodiments similar to those previously described, the SA-SHM coating 30is applied discontinuously along the length of the ribbon 56 and/ordiscontinuously along the length and/or around the circumference of theinner surface of the cable jacket 12 and/or buffer tube 52.

Tables 1-3, below, provide examples of the water absorption capabilitiesof four SA-SHM (referred to individually as “SHM1,” “SHM2,” “SHM3,” and“SHM4”) that can be used as the coatings according to exemplaryembodiments. Certain SA-SHM capabilities are compared against a standardSAP powder (referred to as “SAP1”). In particular, SHM1 is commerciallyavailable as NW1117 from H.B. Fuller Company, Vadnais Heights, Minn.SHM2 is commercially available as NW1120B from H.B. Fuller Company,Vadnais Heights, Minn. SHM3 is commercially available as HM002 fromStewart Superabsorbents, Hickory, N.C. SHM4 is commercially available asHM008 from Stewart Superabsorbents, Hickory, N.C. SAP1 is a powderizedsodium acrylate polymer having particles with average size of about 63microns (commercially available from Stewart Superabsorbents, Hickory,N.C.). All experiments were performed at room temperature of about 22°C.

The data displayed in Table 1 demonstrates the water absorptioncapacities of SHM1 and SHM2 as compared to SAP1. In particular,particles of SAP1 and sections of SEM and SHM2 were placed in a beaker.The masses of each beaker before and after the addition of SAP1, SEM,and SHM2 were determined so as to calculate the amount of each materialadded. A filter as then placed over the beaker, and the mass of thebeaker/material/filter combination was determined. Water was added tothe beaker, and the materials were given time to absorb as much water asthey could. Any remaining, unabsorbed water was drained from the beaker,and the mass of the beaker/material/filter/absorbed water wasdetermined. As can be seen from Table 1, SEM and SHM2 absorbed morewater on a per gram basis than SAP1.

TABLE 1 Water absorption capacity of SHM Materials compared to SAPPowder Material SAP1 SHM2 SHM1 Mass of Beaker + Stir Bar (g) 129.7070.10 136.15 Mass of Beaker + Stir Bar + SHM Material 129.84 70.23136.32 (g) Mass of SHM Material (g) 0.14 0.13 0.17 Mass of Beaker +Filter Assembly (g) 156.80 157.05 150.62 Mass of Beaker + FilterAssembly + Swollen 181.64 179.24 180.56 Gel (g) Mass of Water Absorbed(g) 24.69 22.05 29.76 Mass of Water Absorbed/Mass of SHM 165.69 167.81175.06 Material (g/g)

The data displayed in Table 2 demonstrates the water absorptioncapacities of SHM3 and SHM4 as compared to SAP1. In this experiment, thematerials were placed on a glass slide. Each of the glass slides wereweighed before and after the materials were placed thereon to determinethe mass of each material deposited. Water was then added dropwise onthe materials over a time up to 10 minutes and until it was visuallyobserved that the material was saturated and the extra water drippedoff. The glass slides with gelled material were then weighed todetermine the amount of water absorbed. As can be seen in Table 2, SHM3and SHM4 performed as well or better than SAP1 in terms of waterabsorbed on a per gram basis.

TABLE 2 Water absorption capacity of SHM materials in experiments offilms on glass slide Material SHM3 SHM4 SAP1 Mass of Glass Slide (g)9.272 9.263 9.263 Mass of Glass Slide + Material (g) 9.347 9.348 9.348Mass of Glass Slide + Gelled Material (g) 19.468 19.650 19.650 Mass ofMaterial (g) 0.075 0.085 0.082 Mass of Water Absorbed (g) 10.121 10.30210.305 Mass of Water Absorbed/Mass of Gelled 135.66 121.06 125.67Material (g/g)

The results of a third experiment are provided in Table 3. In thisexperiment, SHM3 was coated onto an optical fiber. The optical fiber wastaped to a glass slide, and SHM3 was applied over the optical fiber. Themass of the optical fiber and glass slide was determined before andafter SHM3 was applied. Water was then introduced to the coated opticalfiber, and the mass of the water absorbed was determined. As can be seenin Table 3, SHM3 performed as well when coating the optical fiber aswhen it was by itself on the glass slide.

TABLE 3 Water absorption capacity of SHM material film on an opticalfiber SHM Material SHM3 Mass of Glass Slide (g) 9.2518 Mass of GlassSlide + Taped Fiber (g) 9.2905 Mass of Glass Slide + Taped Fiber + SHM(g) 9.3075 Mass of Glass Slide + Taped Fiber + SHM + 11.6125 Water (g)Mass of SHM Material (g) 0.017 Mass of Water Absorbed (g) 2.305 Mass ofWater Absorbed/Mass of SHM 135.59 Material (g/g)

FIG. 5 provides a graph of the water swelling capacity of SHM1, SHM2,and SHM3. In this instance, the water swelling capacity was measured interms of the increase in thickness as compared to the original thicknessof the SA-SHM film. As can be seen from the graph of FIG. 5 , SHM1,SHM2, and SHM3 each increased in thickness by more than 100 times theiroriginal thicknesses. Further, SHM1 and SHM3 exhibited a fasterabsorption rate than SHM2. Generally, a faster absorption rate is moreadvantageous for optical fiber cable applications.

Advantageously, embodiments of the optical fiber cable using the SA-SHMcoating on at least one surface or component therein provide the benefitof reducing microbending losses (and thereby optical fiber attenuation)as compared to SAP powders, especially in small size optical fiber cabledesigns. Further, the reduction in microbending can allow for lowercost, more compact cable designs. Moreover, using the SA-SHM coatingprevents sticking of the optical fibers to the buffer tubes and/or ofthe buffer tubes to the jacket in contrast to some optical fiber cablesthat use of SAP gels as a means of water absorption. Additionally, lowercost water-blocking functionality can be provided through the enhancedcontrol of the quantity of SA-SHM used through the length of the cableas compared to SAP coated polyester tapes and yarns and SAP powders. Inaccordance with yet other aspects of the present disclosure, the SA-SHMcan be selectively applied to, for example, the interstices spaces in acable such that attenuation losses may be further reduced.

Indeed, optical fiber cables having a small form factor, such as thoseprovided by embodiments of the SA-SHM coated optical fiber cablesdisclosed herein, allow higher fiber density cable installations andhelp overcome duct congestion issues. Additionally, the cost of suchoptical fiber cables tends to be lower because of the lower materialcost and because they facilitate larger installed lengths during blowingof cables in ducts/micro-ducts.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is in no way intendedthat any particular order be inferred. In addition, as used herein, thearticle “a” is intended to include one or more than one component orelement, and is not intended to be construed as meaning only one.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the disclosed embodiments. Since modifications,combinations, sub-combinations and variations of the disclosedembodiments incorporating the spirit and substance of the embodimentsmay occur to persons skilled in the art, the disclosed embodimentsshould be construed to include everything within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of fabricating an optical fiber cablecomprising the steps of: mixing a superabsorbent, swellable hot meltwith at least one of aluminum trihydrate, magnesium hydroxide, smokesuppressant molybdenum-based particles, or ammonium polyphosphate,pentaerythritol; applying a coating of superabsorbent, swellable hotmelt along at least a portion of a length of an optical fiber; andarranging within a buffer tube a plurality of optical fibers in which atleast one of the plurality of optical fibers is an optical fiber havingthe coating such that a gap between any two adjacent optical fibers isless than a diameter of any one of the plurality of optical fibers. 2.The method of claim 1, further comprising the step of including in thesuperabsorbent, swellable hot melt at least one of sodium or potassiumsodium acrylate or acrylamide copolymers, cross-linked carboxymethylcellulose, ethylene maleic anhydride copolymers, cross-linkedpolyethylene oxide, polyvinyl alcohol copolymers, or starch graftedcopolymers of polyacrylonitrile.
 3. The method of claim 1, wherein thestep of applying the coating of superabsorbent, swellable hot meltfurther comprises applying the coating over 5% to 50% of thecircumference of the optical fiber.
 4. The method of claim 1, whereinthe superabsorbent, swellable hotmelt is capable of absorbing at least50 g of water per gram of superabsorbent, swellable hot melt.
 5. Themethod of claim 1, further comprising the step of applying a coating ofthe superabsorbent, swellable hot melt along at least a portion of alength of the buffer tube.
 6. The method of claim 5, wherein furthercomprising co-extruding the buffer tube with the coating of thesuperabsorbent, swellable hot melt.
 7. The method of claim 6, whereinthe coating of the superabsorbent, swellable hot melt is disposed on aninterior surface of the buffer tube.
 8. The method of claim 6, whereinthe coating of the superabsorbent, swellable hot melt is disposed on anexterior surface of the buffer tube.
 9. The method of claim 1, furthercomprising forming a cable jacket around the buffer tube, wherein acoating of superabsorbent, swellable hot melt is applied to at least aportion of an interior surface of the cable jacket.
 10. The method ofclaim 9, further comprising forming an armor layer around the buffertube, wherein the armor layer is disposed between the buffer tube andthe coating of superabsorbent, swellable hot melt on the interiorsurface of the cable jacket.
 11. A method of fabricating an opticalfiber cable comprising the steps of: applying a coating ofsuperabsorbent, swellable hot melt along at least a portion of a lengthof an optical fiber; and arranging within a buffer tube a plurality ofoptical fibers in which at least one of the plurality of optical fibersis an optical fiber having the coating such that a gap between any twoadjacent optical fibers is less than a diameter of any one of theplurality of optical fibers, wherein applying the coating furthercomprises applying the coating such that sections of coating areseparated by uncoated portions along the length of the optical fiber.12. The method of claim 11, wherein the sections of coating and theuncoated portions each have a length in a range from 1 mm to 100 mm. 13.A method of fabricating an optical fiber cable comprising the steps of:applying a coating of superabsorbent, swellable hot melt along at leasta portion of a length of an optical fiber; and arranging within a buffertube a plurality of optical fibers in which at least one of theplurality of optical fibers is an optical fiber having the coating suchthat a gap between any two adjacent optical fibers is less than adiameter of any one of the plurality of optical fibers, wherein thecoating of superabsorbent, swellable hot melt has a thickness of up to200 microns.
 14. The method of claim 13, wherein the coating ofsuperabsorbent, swellable hot melt has a thickness of at least 1 micron.